The use of mobile communications networks has increased over the last decade. Operators of mobile communications networks have increased the number of base stations in order to meet an increased request for service by users of such networks. The operators of the mobile communications networks wish to reduce the running costs of the base station. It is one option to implement the radio system as an antenna-embedded radio forming an active antenna array of the present disclosure. The antenna-embedded radio may be implemented on a chip, at least for some of the components of the antenna-embedded radio. The antenna-embedded radio reduces space needed to house the hardware components of the base station. Power consumption during normal operation of the active antenna array is reduced when implementing the active antenna array using one or more chips.
Mobile communications networks use protocols when relaying radio signals. Examples of protocols for mobile communications system include the GSM protocol but are not limited thereto.
New types of protocols for radio signals (or pertaining to radio signals) in mobile communication networks have been developed in order to meet an increased need of mobile communication and to provide higher data rates to hand sets as well as an increased flexibility in adapting radio signals relayed by the active antenna array to specific needs of an individual site or cell of the mobile communications network.
An example for a newer type of protocol for protocol radio signals is the unified mobile telecommunication service protocol (UMTS), third generation long term evolution (3GLTE) protocol, freedom of mobile multi media access radio (FMRA) protocol, wideband code division multiple access (WCDMA) protocol, and Worldwide Interoperability for Microwave Access (WiMAX) but is not limited thereto.
Radio signals using the first type of protocol shall be referred to herein as first protocol radio signals. Radio signals using the second newer type of protocol shall be referred to herein as second protocol radio signals.
The operators of the mobile telecommunications networks are interested in supporting the first protocol radio signals and the second protocol radio signals. Therefore an interest exists to provide active and/or passive antenna arrays relaying both the first protocol radio signals and the second protocol radio signals.
The second protocol radio signals often require flexibility in beam shaping not often required with the first protocol radio signals.
In the prior art it was possible to provide an active antenna array for the second protocol radio signals and a further antenna array relaying the first protocol radio signals. Such an approach is rather expensive for the operators of the mobile communications network as two separate sets of antenna arrays need to be setup and maintained.
Combined passive antenna arrays for mobile communication networks are known that relay both the first protocol radio signals and the second protocol radio signals concurrently. These combined antenna arrays of the prior art unfortunately do not provide the increased flexibility in terms of beam shaping as is often required with active arrays.
FIG. 1 shows a passive antenna array 1a of the prior art. The passive antenna array 1a of the prior art is adapted to relay two different air interface standards. One of the air interface standards is the first protocol, for example GSM or UMTS but not limited thereto, and another one of the air interface standards is the second protocol, for example UMTS, but is not limited thereto.
The first protocol radio signal comprises a general first protocol transmit signal 70Tx and a general first protocol receive signal 70Rx. The second protocol radio signal comprises a general second protocol transmit signal 75Tx and a general second protocol receive signal 75Rx. The general first protocol transmit signal 70Tx and the general first protocol receive signal are present between a first protocol base transceiver station (BTS) 10-1 and a duplexer 20. The general second protocol transmit signal 75Tx and the general second protocol receive signal 75Rx are present between a second protocol base transceiver station (BTS) 10-2 and the duplexer 20. The duplexer 20 combines the general first protocol transmit signal 70Tx and the general second protocol transmit signal 75Tx with a low combiner loss. The low combiner loss is much lower than a loss present with a −3 dB hybrid or Wilkinson combiner. It is a disadvantage of the duplexer 20 to require a roll-off band between the general first protocol transmit signal 70Tx and the general second protocol transmit signal 75Tx as well as between the general first protocol receive signal 70Rx and the general second protocol receive signal 75Rx. The duplexer 20 separates a general first protocol receive signal 70Rx and a general second protocol receive signal 75Rx such that the general first protocol receive signal 70Rx reaches the first protocol BTS 10-1 and the general second protocol receive signal 75Rx reaches the second protocol BTS 10-2.
The required roll-off wastes bandwidth as the roll-off band is within bandwidth of the first protocol radio signals and bandwidth of the second protocol radio signals. Therefore it is expensive to use the duplexer 20 in terms of spectrum license fees, as the license fees also need to be paid for the roll-off band of the duplexer 20. The duplexer 20 is further inflexible with respect to frequency bandwidths for the first protocol radio signals and the second protocol radio signals. The bandwidth allocated to the first protocol radio signal and a bandwidth allocated to the second protocol radio signal are in the prior art fixed.
A DC voltage adder 215 is located between the duplexer 20 and a tower mounted amplifier (TMA) 80. The DC voltage adder 215 is capable of adding a DC voltage to a signal path relaying radio frequency signals. The advantage of using the DC voltage adder 215 between the duplexer 20 and the TMA 80 is that a length of a DC connection from a first DC voltage supply 202 to the TMA 80 can be reduced. Typically the TMA 80 is mounted on a tower. Hence the cable from the duplexer 20 to the TMA 80 may be several meters long or even substantially longer. It will be appreciated that long DC lines add to overall costs of the active antenna array and may be vulnerable to any radio frequency (RF) impinging thereon.
The DC voltage adder 215 may be implemented using the bias T as known in the art, or so called RF chokes using an inductance tailored such that RF frequency travelling along the coaxial cable may not pass via the DC voltage adder 215 back into the DC supply 202. Conversely, the first DC voltage 205 is capable of passing through the DC voltage adder 215. The DC voltage adder 215 is of low impedance to the DC voltage but of high impedance to any RF signal relayed along the coaxial cable. Typically the duplexer 20 does not have DC conductivity. Hence the DC voltage adder 215 needs to be present downstream of the duplexer 20. Otherwise the first DC voltage 205 provided by the first DC voltage supply 202 will not reach the TMA 80 from which the DC voltage is supplied to power amplifiers or any other active components within the TMA 80.
A passive feeder network forwards the general first protocol transmit signal 70Tx and the general second protocol transmit signal 75Tx from the TMA 80 to the antenna array 1. The passive feeder network further forwards a general first protocol receive signal 70Rx, and the second protocol receive signal 75Rx from the passive antenna array 1a to the TMA 80. The general first protocol transmit signal 70Tx is split into individual first protocol transmit signals 70Tx-1, 70Tx-2, . . . , 70Tx-N at a port 11 of the antenna array 1a reaching an individual one of the antenna elements Ant-1, Ant-2, . . . , Ant-N of the antenna array 1a. In FIG. 1 only 16 of the antenna elements Ant-1, Ant-2, . . . , Ant-N are shown. A corporate feed network may be used for splitting the general first protocol transmit signal 70Tx into the individual first protocol transmit signals 70Tx-1, 70Tx-2, . . . , 70Tx-N. The corporate feed network is illustrated in FIG. 1 by the thick black lines within the body of the passive antenna array 1a. The individual first protocol transmit signal 70Tx-1, 70Tx-2, . . . , 70Tx-N is only shown for the individual antenna elements Ant-1 and Ant-16 in FIG. 1 for the sake of clarity. The individual transmit signal 70Tx-1, 70Tx-2, . . . , 70Tx-N is typically present for each one of the antenna elements Ant-1, Ant-2, . . . , Ant-N. It is also conceivable that the individual first protocol transmit signals 70Tx-1, 70Tx-2, . . . , 70Tx-N are not present for each of the antenna elements Ant-1, Ant-2, . . . , Ant-N. In this case not all of the antenna elements Ant-1, Ant-2, . . . , Ant-N are transmitting.
The general second protocol transmit signal 75Tx is split into a plurality individual second protocol transmit signals 75Tx-1, 75Tx-2, . . . , 75Tx-N reaching the individual antenna element Ant-1, Ant-2, . . . , Ant-N of the antenna array 1a. The individual second protocol transmit signal 75Tx-1, 75Tx-2, . . . , 75Tx-N is only shown for the individual antenna elements Ant-1 and Ant-16 in FIG. 1 for the sake of clarity but may be present for more than two of the antenna elements Ant-1, Ant-2, . . . , Ant-N.